1. Field of the Invention
This invention relates in general to data readout from a disc and, in particular, to a correct determination of an angular position of a disc. More specifically, but without restriction to the particular embodiments hereinafter described in accordance with the best mode of practice, this invention relates to methods for triggering through interrupted grooves and related optical analysis discs and systems.
2. Discussion of the Background Art
The Optical Bio-Disc, also referred to as Bio-Compact Disc (BCD), bio-optical disc, optical analysis disc, or compact bio-disc, is now known in the art for performing various types of biochemical analyses. In particular, this optical disc utilizes the laser sou28 1 rce of an optical storage device to detect biochemical reactions on or near the operating surface of the disc itself.
The readout of specific, localized target analysis regions on an optical reader requires that on successive rotations of the disc, either the data are captured from the same angular positions on the disc, or that the correct regions are identified after data capture.
Both require that the angular positions be recognized by the reader to sub-micron accuracy, preferably below 0.3 μm. Errors in the angular position result in misplacement of the successive lines, and therefore noise and distortions in the reconstructed image.
The discs considered have grooves that are used for generating tracking signals, the rotation of the disc resulting in the laser spot being at an increased radius of one track pitch per rotation.
In order to determine the angular position on each rotation, marks are made on the disc in either the operational layer of the disc, or on the other non-operational surfaces. Considering marks to be recognized on the operational surface, although information can be written into the grooves, these cause a reduction in reflected light intensity and can be confused with other causes of reduced light reflection, e.g. dirt etc. Therefore there is inaccuracy in determining the exact position of the mark, and error in the triggering.